At present, Atomic Absorption Spectrometry with electrothermal atomization is one of the most developed methods of determination of trace quantities of more than 60 elements in a variety of substances and materials. High sensitivity, selectivity and precision are characteristic of the method. An inherent feature of this method of analysis is non-stationarity of the analytical signal. All modern spectrophotometers record it with high temporal resolution; however, the signal recorded by a photomultiplier tube (PMT) at the instrument output is essentially an integrated characteristic of analytical volume as a whole and lacks spatial resolution. In the case of a uniform distribution of analyte atoms in the atomizer volume this causes no problems. However, as the imaging of analytical volume has shown, the atoms and molecules of the element to be determined may be distributed within the electrothermal atomizer extremely non-uniformly (1)A. Kh. Gilmutdinov, Yu. A. Zakharov, V. P. Ivanov and A. V. Voloshin. Shadow Spectral Filming: A method of investigating Electrothermal Atomization. Part 1. Dynamics of Formation and Structure of the Absorption Layer of Thallium, Indium, Gallium and Alluminium Atoms. // Journ. Anal. Atom. Spectrometry, 1991, v. 6, p.505-519, (2) A. Kh. Gilmutdinov, Yu. A. Zakharov, V. P. Ivanov, A. V. Voloshin and K. Dittrich. Shadow Spectral Filming: A method of investigating Electrothermal Atomization. Part 2 Dynamics of Formation and Structure of the Absorption Layer of Tallium, Indium, Gallium and Alluminium Molecules. // Journ. Anal. Atom. Spectrometry, 1992, v. 6, p. 675-683.!. On the other hand, theoretical analysis (3) A. Kh. Gilmutdinov, T. M. Abdullina, S. F. Gorbachev and V. L. Makarov. Formation of Analytical Signal in Electrothermal Atomic Absorption Spectrometry. Influence of temperature and concentration gradients. // Zhurn. Analit. Khimii, 1991, v. 46, p. 1480-1492.! shows that the analytical signal recorded at the spectrophotometer output depends not only on the number of absorbing atoms, but also on their distribution over the atomizer cross-section. This leads to two limitations in the existing detection systems. First, the relation between the absorbance recorded at the spectrophotometer output and the number of absorbing atoms proves to be ambiguous. Second, analytical curves appear to be largely curved in the region of high absorbances 3!.
Thus, the use in an AA spectrophotometers of a detection system having no spatial resolution leads to narrowing of the range of concentrations to be measured due to curvature of analytical curves and to the increase of measurement error due to the ignored influence of absorption layers inhomogeneity. Therefore, to obtain a correct analytical signal, it is necessary to have a detection system ensuring not only sufficient temporal but also spatial resolution.
There exist a detection system of a AA spectrophotometer with a linear photodiode array detector (4) Gary P. Moulton, Thomas C. O'Haver, James M. Harnly Continuum Source Atomic Absorption Spectrometry with a Pulsed Source a Photodiode Array Detector. // Journ. Anal. Atom. Spectrometry, 1989, v. 4, p. 673-674.!. In such a system the photodiode detector is positioned along the spectral instrument dispersion and besides the resonance line also records the radiation of adjacent lines.
However, such an arrangement of the photodiode array detector offers no possibility to use it for spatially resolved recording of the analytical signal. Therefore, such spectrophotometers have no spatial resolution and suffer from the drawbacks similar to the above shortcomings inherent in detection systems based on the use of photomultiplier tubes.